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Driving home in my 2014 X5 35i xdrive turned on my windshield defrost fan kicks on like its trying to take off oil temperature is not even registering noticed power loss. Parked car turned off and on fan stopped spinning up drove a little got error U1408, P0128 (cooling temp below thermostat regulating pressure). Got home banged on the thermostat drove a few more miles error cleared been driving ever since coolant temperature is 71 - 78c monitoring through obc menu. Of course my warranty ended December 6, 2019 so i am on the hook for this one. I was a cold day in CA i was driving through some weather with wind temp probably around 36F could this be a one time event or a sign of failure? Should I change the thermostat? Been suggested by several independent shops to change electric water pump is that true? Also notice when i turn on my windshield defogger coolant temp drops dramatically 10 - 15c.

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How many miles?

There's a video on YouTube you should watch concerning how BMW engineers these systems to let you know that somethings going bad way before a catastrophe failure that leaves you stranded. I try to find it & post later.

Found it. Here's a good video from a BMW enthusiast that had posted MANY DIY repair/modification videos. Hope you enjoy...the 1st two minutes are just his "fun" drive on his new bimmer; you can skip that part.
https://youtu.be/BZt4qLEDDkw

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Thanks very relevant information! Car has 70k miles on it.
@ecxone87......from what I have read on this & E70 forum, these electric water pumps can start to go from 70k to 90k. It might be prudent to be looking/planning for a new water pump, thermostat & related hoses; as a preemptive/preventive repair. I don't know if you do any DYI or not but this could be a good weekend project if it's not your only vehicle.

Here's a video on replacing the thermostat

https://youtu.be/58qk7p12fVY

The electric water pump is a little more work & difficult but I only found E70 videos, which would be similar.
 
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